As a processing apparatus configured to process a substrate, there is a batch type substrate processing apparatus including a vertical-type reaction furnace, a boat that is a substrate retaining mechanism configured to retain a predetermined number of processing substrates (hereinafter referred to as wafers) in a horizontal position in multiple stages, and a substrate transfer machine configured to transfer the wafers into the boat, and processing the wafers in the reaction furnace while the wafers are retained in the boat.
Conventionally, a wafer crack detection mechanism is installed for detecting an abnormality of the wafer in the substrate processing apparatus so that substrate processing is not continued in a state in which the abnormality occurs in the wafer when the abnormality such as a crack, warp, or misalignment occurs in the wafer due to thermal stress during heating in the reaction furnace, and during cooling when the wafer is taken out from the reaction furnace.
As disclosed in WO2005/31851 A, in a wafer crack detection function, a photoelectric sensor arranged in a horizontal direction at a position at which a wafer end face is detected is moved at a constant speed in a vertical direction with respect to a boat to which the wafer is transferred, and a state of the wafer is determined from a change in the amount of light during the movement.
In addition, according to JP 2013-212723 A, the change of the amount of light at a position exceeding the threshold value (slightly low) and a position being out of the threshold value (slightly high) with respect to a prescribed threshold value and a position in which the value becomes maximum (peak) are obtained and used for determination. As for a reference value to be used for determination of a wafer state, data of the slightly high, slightly low, and peak of each slot on the boat are obtained in a state in which a normal wafer is arranged, and are retained by a system as master data. When wafer crack detection is executed, the data are obtained of the slightly high, slightly low, and peak of each slot, and differences from the master data are calculated. When the difference from the master data exceeds an allowed value set in the system, it is determined that there is the abnormality, and it becomes a wafer abnormality detection state. Here, the allowed value of the difference from the master data is common in all slots, and a product wafer is used as a reference.
Further, there is a substrate processing apparatus in which a ring-shaped retaining member is mounted on the boat, and the wafer is placed on the retaining member in order to improve process performance condition. For example, according to JP 2013-212723 A, a function is described of detecting in advance a deformation or misalignment to the retaining member, in order to solve a problem that the wafer crack detection mechanism cannot be used, since the retaining member exists on the optical axis of the wafer crack detection mechanism, and the retaining member affects the waveform of the amount of light, in a state in which the retaining member is mounted on the boat.
Currently, it is necessary to strictly determine distortion for the product wafer. On the other hand, a dummy wafer is required to be used repeatedly even when some distortion or warp. Here, even in JP 2013-212723 A, it is disclosed that the allowed value for other wafers including the dummy wafer can be set on the basis of the product wafer. However, content of JP 2013-212723 A does not sufficiently respond to a solution of the above problem, the solution improving an apparatus operation rate by repeatedly using the dummy wafer and extending a replacement cycle of the dummy wafer.